1. Field of the Invention
The present invention relates to a light receiving element and, more particularly, a light receiving element for position detection, and a sensor and an electronic apparatus having the same.
2. Description of the Background Art
Light receiving elements for position detection are used for a sensor or the like which detects a position of an object to be measured that reflects a light or the like based on a position of incidence of the light or the like in a light receiving element.
For example, Japanese Patent Laying-Open No. 59-056774 (Patent Literature 1) discloses a position detection device having such a light receiving element as described in the following. More specifically, in a position detection device in which on one of the surfaces of a semiconductor substrate of a certain conductivity type, a resistance layer of an opposite conductivity type is provided, and a converted current generated by corpuscular rays or the like which enter the resistance layer is divided by the resistance layer and extracted from a plurality of electrodes to detect a position of incidence of the corpuscular rays or the like, the resistance layer is surrounded by four resistance lines formed of a circular arc so as to have a connection point of the resistance line located at each angle of a square or a rectangle, an arithmetical circuit is provided which extracts a current from the connection point of the resistance line and operates the extracted current to obtain an output related to the position of incidence of the corpuscular rays or the like, and a predetermined relationship is given between a sheet resistivity of the resistance layer and the resistance line formed of a circular arc.
In addition, Japanese Patent Laying-Open No. 61-108930 (Patent Literature 2) discloses a position detection device having such a light receiving element as described in the following. More specifically, in a position detection device in which on a semiconductor substrate having a first conductivity type, a resistance layer of a second conductivity type is formed and a current generated by corpuscular rays or the like which enter the semiconductor substrate is divisionally output from a plurality of electrodes provided on the periphery of the resistance layer, the corpuscular rays or the like are made to enter from the side of the semiconductor substrate opposite to the surface on which the resistance layer of the second conductivity type is formed, a layer of the first conductivity type whose thickness is small enough and whose concentration is high is formed on the surface of the semiconductor substrate which corresponds to the surface of incidence, the resistance layer is configured to be surrounded by four resistance lines formed of a circular arc so as to have a connection point of the resistance line located at each angle of a square or a rectangle such that a current is extracted from the connection point of the resistance line, and a predetermined relationship is given between a sheet resistivity of the resistance layer and the resistance line formed of a circular arc.
In the position detection devices having a light receiving element recited in Patent Literature 1 and Patent Literature 2, however, in order to increase an S/N (Signal to Noise) ratio of a position signal indicative of a position of incidence of a light or the like in the light receiving element, that is, to increase an output current difference derived from a difference in a position of incidence of the light, a resistance layer whose sheet resistivity is extremely high should be formed. This is because when the sheet resistivity is low, variation in a sheet resistivity in each region of the resistance layer largely affects an output current to make accurate position detection difficult. Furthermore, in order to increase the S/N ratio of the position signal, a resistance layer whose sheet resistivity is highly uniform in the whole region of the semiconductor substrate should be formed.
Forming a resistance layer whose sheet resistivity is extremely high and making the sheet resistivity be uniform in the whole region of the semiconductor substrate is difficult in terms of a manufacturing process. In addition, although for increasing the sheet resistivity, an impurity concentration of the resistance layer should be decreased, decreasing the impurity concentration of the resistance layer will result in becoming liable to be affected by surface charges generated during the manufacturing process and surface charges generated according to environments of use. As a result, the sheet resistivity varies to cause characteristic variation, that is, variation in a sheet resistivity due to temperature and mobile ions or the like. The position detection devices having a light receiving element recited in Patent Literature 1 and Patent Literature 2 therefore have a drawback of difficulty in increasing an S/N ratio of a position signal in terms of a manufacturing process.